Xiali Fm
Type Locality and Naming
It was named by Bai Shenghai in 1989. The naming section is located at the Yanshiping Flat by the Qinghai-Tibet Highway within the territory of Qinghai Province, with its reference section being situated 7 km southeast of the Qoimaco, the Tanggula−Mts Township, Germu (Golmud) City, Qinghai Province (Regional Survey Party of Qinghai Province, 1987). Schematic strat column in previous "red Chinese Lexicon" suggests it is the upper-middle formation in the Yanshiping Gr.
Synonym: （夏里组）
Lithology and Thickness
Composed of grey, grey-green and violet sandstones, siltstones and calcareous and argillaceous siltstones, intercalated with several layers of oolitic limestones and mudstones, locally with micro-conglomerate and gypsum, with cross-beddings and ripple marks being found frequently. The formation is 646 m thick.
Relationships and Distribution
Lower contact
Being composed of grey and violet sandstone and siltstone, the basal part of the formation is in a conformable contact with the underlying Buqu Fm. It is in a conformable contact with its underlying strata in most regions.
Upper contact
Only in the area of Ri’aronggongma, eastern bank of Chibuzhangco, Cojuri and to the west of Meidutang is the formation in an unconformable contact with the overlying lower Cretaceous Conglomerate Fm, or the Neogene Volcanic Rock Fm, Sandy Conglomerate Fm. Regionally, the next younger unit on schematic strat column is indicated as a Wasuo Fm (not yet in the provided Jurassic entries).
Regional extent
The formation is distributed in the form of a belt extensively in the Chibuzhangco area, on the southern slope of the Zurkenwula Mts to the north of the Qoimaco and Saiduogangri area, with a consistent lithology, and with a thickness of 400-646 m.
GeoJSON
Fossils
It yields bivalve fossils such as Protocardia striatula, Modiolus bipartilus, Pteroperna burensis, Astare multiformis, Anisocadia tenera, Plagiostoma cf. rigida, Chlamys (C.) splendens, Isognomon (Mytiloperna) cf. bergeroni, Myopholas acuticostata and Solemya woodwardiana, as well as Brachiopod fossils as represented by Stenogmus pentagonalis and Ivanoviella cf. steinbessi. Dinoflagellate Tubotuberella egemenii Assemblage Zone was reported in the Wenquan Section (Cheng and He, 2006).
Age
Depositional setting
It is interpreted as shallow-marine environment.
Additional Information